Cytokines typically exert their respective biochemical and physiological effects by binding to specific receptor molecules. Receptor binding will then stimulate specific signal transduction pathways (Kishimoto, T., et al., Cell 76:253-262 (1994). The specific interactions of cytokines with their receptors are often the primary regulators of a wide variety of cellular process including activation, proliferation, and differentiation (Arai, K.-I, et al., Ann. Rev. Biochem. 59:783-836 (1990); Paul, W. and Seder, R., Cell 76:241-251 (1994)).
Human interleukin (IL)-17 was only recently identified. IL-17 is a 155 amino acid polypeptide which was molecularly cloned from a CD4+ T-cell cDNA library (Yao, Z., et al., J. Immunol. 155:5483-5486 (1995)). The IL-17 polypeptide contains an N-terminal signal peptide and contains approximately 72% identity at the amino acid level with a T-cell trophic herpesvirus saimiri (HVS) gene designated HVS13. High levels of IL-17 are secreted from CD4-positive primary peripheral blood leukocytes (PBL) upon stimulation (Yao, Z., et al., Immunity 3:811-821 (1995)). Treatment of fibroblasts with IL-17, HVS13, or another murine homologue, designated CTLA8, activate signal transduction pathways and result in the stimulation of the NF-kappaB transcription factor family, the secretion of IL-6, and the costimulation of T-cell proliferation (Yao, Z., et al., Immunity 3:811-821 (1995)).
An HVS13-Fc fusion protein was used to isolate a murine IL-17 receptor molecule which does not appear to belong to any of the previously described cytokine receptor families (Yao, Z., et al., Immunity 3:811-821 (1995)). The murine IL-17 receptor (mIL-17R) is predicted to encode a type I transmembrane protein of 864 amino acids with an apparent molecular mass of 97.8 kDa. mIL-17R is predicted to possess an N-terminal signal peptide with a cleavage site between alanine-31 and serine-32. The molecule also contains a 291 amino acid extracellular domain, a 21 amino acid transmembrane domain, and a 521 amino acid cytoplasmic tail. A soluble recombinant IL-17R molecule consisting of 323 amino acids of the extracellular domain of IL-17R fused to the Fc portion of human IgG1 was able to significantly inhibit IL-17-induced IL-6 production by murine NIH-3T3 cells (supra).
Interestingly, the expression of the IL-17 gene is highly restricted. It is typically observed primarily in activated T-lymphocyte memory cells (Broxmeyer, H. J. Exp. Med. 183:2411-2415 (1996); Fossiez, F., et al., J. Exp. Med. 183:2593-2603 (1996)). Conversely, the IL-17 receptor appears to be expressed in a large number of cells and tissues including (Rouvier, E., et al., J. Immunol. 150:5445-5456 (1993); Yao, Z., et al., J. Immunol. 155:5483-5486 (1995)). It remains to be seen, however, if IL-17 itself can play an autocrine role in the expression of IL-17. IL-17 has been implicated as a causitive agent in the expression of IL-6, IL-8, G-CSF, Prostaglandin E (PGE2), and intracellular adhesion molecule (ICAM)-1 (Fossiez, F., supra; Yao, Z., et al., Immunity 3:811-821 (1995)). Each of these molecules possesses highly relevant and potentially therapeutically valuable properties. For instance, IL-6 is involved in the regulation of hematopoietic stem and progenitor cell growth and expansion (Ikebuchi, K., et al., Proc. Natl. Acad. Sci. USA 84:9035-9039 (1987); Gentile, P. and Broxmeyer, H. E. Ann. N.Y. Acad. Sci. USA 628:74-83 (1991)). IL-8 exhibits a myelosuppressive activity for stem and immature subsets of myeloid progenitors (Broxmeyer, H. E., et al., Ann. Hematol. 71:235-246 (1995); Daly, T. J., et al., J. Biol. Chem. 270:23282-23292 (1995)). G-CSF acts early and late to activate and stimulate hematopoiesis in general (more specifically, neutrophil hematopoiesis) while PGE2 enhances erythropoiesis, suppresses lymphopoiesis and myelopoiesis in general, and strongly suppresses monocytopoiesis (Broxmeyer, H. E. Amer. J. Ped. Hematol./Oncol. 14:22-30 (1992); Broxmeyer, H. E. and Williams, D. E. CRC Crit. Rev. Oncol./Hematol. 8:173-226 (1988)).
IL-17 receptor appears to be structurally unrelated to any previously described cytokine receptor family. Despite the existence of 12 cysteine residues in the extracellular domain, their relative positions are not characteristic of receptor molecules classified as members of the immunoglobulin superfamily (Williams, A. and Barclay, A. Annu. Rev. Immunol. 6:381-405 (1988)), the TNFR family (Smith, C., et al., Science 248:1019-1023 (1990)), the hematopoietin receptor family (Cosman, D. Cytokine 5:95-106 (1993)), or any previously described tyrosine kinase receptors (Hanks, S., et al., Science 241:42-52 (1988)).
Thus, there is a need for polypeptides that function as receptor molecules for cytokines and, thereby, function in the transfer of an extracellular signal ultimately to the nucleus of the cell, since disturbances of such regulation may be involved in disorders relating to cellular activation, hemostasis, angiogenesis, tumor metastasis, cellular migration and ovulation, as well as neurogenesis. Therefore, there is a need for identification and characterization of such human polypeptides which can play a role in detecting, preventing, ameliorating or correcting such disorders.